The present invention relates to a system for filling slab-gel holders with coagulable solution which subsequently solidifies into the gel form. For purposes of this application, the term "coagulable solution" is intended to comprehend both monomer solutions and colloidal sols that are capable of polymerizing or coagulating to form gels. Also the term "coagulate" is intended to include the processes of monomer polymerization and that of sol coagulation to produce gels. The gels are often provided with a density gradient across the slab. These gradient gels are prepared by filling the holder with a coagulable solution flow of continually changing density. The liquid fill for the gradient gels is therefore termed a gradient solution or merely a gradient.
The gels are used for electrophoresis separation of material such as protein; protein subunits and nucleic acids. Such separations are often the second separation in a two-dimensional separation system. The procedure begins with the isoelectric separation of species along a thin, elongated or spaghetti-like gel medium. In this original separation, the proteins, amino acids or other species migrate to a previously established pH point within the gel at which the sample is electrically neutral. These separations are quite well known and can be followed by a second dimensional electrophoresis separation to provide a high resolution of protein and protein subunits. In the electrophoresis separation, sample species migrate through a gel acting as a sieve to a point determined by their molecular weight.
The initial isoelectric separation and the second electrophoresis separation are both more fully described in the assignee's U.S. Pat. 4,088,561 filed May 1978, by Norman L. Anderson, entitled "Apparatus for Electrophoresis Separation." This application is expressly incorporated herein by reference. The electrophoresis separation is performed across an acrylamide gel containing sodium dodecyl sulfate (SDS) employed to negate the isoelectric effect. Gel compositions are well known and include polymerization as well as cross linking agents along with a gel buffer. Gels of thess types have previously been assembled manually between glass plates with laboratory clamping devices and subjected to electric current between separate upper and lower buffer solutions. Previous filling operations ordinarily were performed one at a time and then transferred to the apparatus for conducting the electrophoresis separation. These procedures are quite cumbersome and time-consuming when a large number of samples must be run, as in genetic screening surveys and clinical diagnostic applications. The prior art devices for the filling of the slab-gel holders have generally provided for filling from the top which may promote intermixing of gradient portions of different density. Prior to coagulation, the solution, sealed in by agar, has tended to leak and make the process more difficult to accomplish.